The patent literature describes numerous processes and agents intended for the demolding of polymeric injection moldings. These descriptions extend from the spraying of the inner sides of the injection mold with lubricants, such as oils, fats, talc, waxes or silicone oils, to addition of lubricants to the polymer, where these simultaneously serve as an aid to demolding. Both these processes, the spraying of the inner surfaces of the injection molds with oily chemicals and procedures of admixture to the bulk material, have serious disadvantages. The introduction of a spray onto the inner walls of the injection mold generally brings about good demoldability, but has the disadvantage that there are oily, liquid substances located on the surfaces of the injection moldings after demolding. Prior to use or further processing of the injection moldings, therefore, the demolding auxiliary very generally has to be removed, e.g. by means of a solvent. Considerable process resources and costs are required for separation of solvent and demolding auxiliary, e.g. by distillation, and then to permit recycling of the substances in order to minimize pollution of the environment.
A still greater disadvantage is present when lubricants or mold-release agents are added to the actual polymer used for the injection-molding process. Frequently, no effects are measurable unless more than 0.1% by weight of mold-release agents is added, based on the total weight of the polymer. This addition results in very high costs for the starting materials. Additions of this order of magnitude moreover often alter the properties of the polymer materials, e.g. tensile strength, melting point, etc., and this can imply additional alterations or modifications to the mixing specification.
The use of inorganic particles, in particular silicas, as antiblocking or anticaking agents during the production of polymer films has been known for some time (Technical Bulletin Pigments No. 13: Synthetic Silicas as Auxiliaries for the Plastics Industry, 5th edition, Degussa A G, August 1992). In these applications, a silica powder, e.g. Aerosil R 972 or Sipernat 44, is either incorporated into the polymer prior to its processing or mixed with polymer pellets before these pellets are processed, e.g. by blow molding, injection molding, or extrusion. Polymer films produced in this way do not block, for example when they are wound up. These uses of silicas probably also affect the demolding properties of the polymers used to some extent, but the use of the silicas as additives is relatively complicated, since the polymers or polymer pellets have to be mixed with the silica prior to the actual molding process.